The present invention generally relates to processes for the thermal cracking of hydrocarbons and, specifically, to a method for increasing the yield of hydrocarbons having five or more carbon atoms in a process for the thermal cracking of hydrocarbons.
In a process for producing an olefin compound, a fluid stream containing a saturated hydrocarbon such as ethane, propane, butane, pentane, naphtha, or mixtures of two or more thereof is fed into a thermal (or pyrolytic) cracking furnace. A diluent fluid such as steam is usually combined with the hydrocarbon feed material being introduced into the cracking furnace.
Within the furnace, the saturated hydrocarbon is converted into an olefinic compound. For example, an ethane stream introduced into the cracking furnace is converted into ethylene and appreciable amounts of other hydrocarbons. A propane stream introduced into the furnace is converted to ethylene and propylene, and appreciable amounts of other hydrocarbons. Similarly, a mixture of saturated hydrocarbons containing ethane, propane, butane, pentane and naphtha is converted to a mixture of olefinic compounds containing ethylene, propylene, butenes, pentenes, and naphthalene. Olefinic compounds are an important class of industrial chemicals. For example, ethylene is a monomer or comonomer for making polyethylene. Other uses of olefinic compounds are well known to those skilled in the art.
As a result of the thermal cracking of a hydrocarbon, the cracked product stream can also contain appreciable quantities of hydrogen, methane, acetylene, carbon monoxide, carbon dioxide, and pyrolytic products other than the olefinic compounds.
In thermal or pyrolytic cracking processes, saturated hydrocarbons, particularly hydrocarbons having less than five carbon atoms, are converted from higher molecular weight compounds to lower molecular weight compounds. In the case of ethane cracking, ethane is converted to lower molecular weight ethylene. But, the cracking of ethane also results in the conversion of ethane to such undesirable lighter compounds as hydrogen, methane, and acetylene. Desirable compounds other than the ethylene produced by the cracking of ethane are hydrocarbons having at least five carbon atoms. Because of the lower value of the undesirable lighter compounds relative to hydrocarbons having at least five carbon atoms, it is preferred and can be economically beneficial to increase the production of the more desirable compounds at the expense of an offsetting reduction in the production of the undesirable lighter compounds.
It is thus an object of this invention to provide an improved process for cracking saturated hydrocarbons to produce olefinic end-products.
Another object of this invention is to provide a process for enhancing the yield of hydrocarbons having at least five carbon atoms in a process for cracking saturated hydrocarbons.
A still further object of this invention is to improve the economic efficiency of operating a cracking process for cracking saturated hydrocarbons by shifting the production of light ends to the production of hydrocarbons having at least five carbon atoms.
In accordance with one embodiment of the invention, a tube of a cracking furnace is contacted with a composition containing a tin compound and a silicon compound to thereby provide a treated tube. The treated tube is charged with a saturated hydrocarbon stream while the treated tube is being operated under suitable conditions for cracking the saturated hydrocarbon stream to produce a product stream having a concentration of hydrocarbon compounds having at least five carbon atoms. A portion of the concentration of hydrocarbon compounds having at least five carbon atoms is recovered.
Another embodiment of the invention includes a method for incrementally increasing the yield of hydrocarbon compounds having at least five carbon atoms in a product stream produced by a thermal cracking process for cracking a saturated hydrocarbon stream. A composition containing a tin compound and a silicon compound is added to the saturated hydrocarbon stream during cracking under suitable cracking conditions. A portion of the incremental yield of hydrocarbons having at least five carbon atoms is thereafter recovered.